Breathing is controlled by your autonomic or involuntary nervous system. Although you have limited conscious control over breathing, such as you can choose to hold your breath, once carbon dioxide levels begin to rise in your blood, your reflexes take over and you are going to breathe. Exercise has a significant impact on all aspects of your breathing.
Mechanics of Breathing
When your diaphragm and your intercostals, or rib muscles, contract, air is drawn into your nose or mouth, down your pharynx, larynx and trachea, through your bronchi and into your lungs. As these muscles relax, air is pushed up and out of your lungs and you exhale. Breathing out requires no effort on your part and relies on the elasticity of your respiratory muscles, but you can forcefully exhale by compressing your abdominal cavity by contracting your abdominals.
Diffusion
You lungs are made up from lots of tissue bundles that look like bunches of grapes called alveoli. At the alveoli, oxygen is absorbed into your blood for circulation around your body and carbon dioxide is removed from your blood and exhaled. This process is called diffusion or gaseous exchange. At rest, your normal breathing rate is around six breaths per minute, but when you exercise, this can rise significantly--up to 30 breaths or more.
Increased Demand for Oxygen
Like most animals, your body requires a constant supply of oxygen. When you are calm and still, you need approximately 6 liters of oxygen per minute to keep you alive and functioning. When you exercise, the demand for oxygen increases significantly and can rise to 60 liters or more, depending on your fitness. To facilitate such a large amount of oxygen, breathing rate and depth, called tidal volume, increase, which results in an increase in minute ventilation--the measure of how much air passes in and out of your lungs in 60 seconds.
Exercise and Breathing Rate
As you get fitter, your breathing rate slows down. This happens because your lung function improves. Each breath you take becomes more voluminous, which means that you don't need to breathe as often to process the same amount of air at rest. Your breathing muscles--the intercostals and diaphragm--become stronger and there is an increase in capillary density at your alveoli to allow for greater diffusion of oxygen into your blood and removal of carbon dioxide from your blood.
Conditions Affecting Lung Function
Exercise has a positive effect on lung function, but there are a number of conditions that affect the lungs and may cause breathing problems while exercising. The most common lung condition is asthma, which causes the airways to close up--termed vasoconstriction. This makes it very difficult to get oxygen into the lungs for diffusion. Asthma sufferers often use inhalers that relax the airways to allow regular breathing to resume.
References
- "Exercise for Heart and Health"; Barbara J. Fletcher, Gerald F. Fletcher, John D. Cantwell and John Presotti; 2008
- "Principles of Anatomy & Physiology, Ninth Edition"; Sandra R. Grabowski and Gerald J. Tortora; 2000
- "Anatomy of Exercise: A Trainer's Inside Guide to Your Workout"; Pat Manocchia; 2009
